Fudamental Research And Production Simulation Of Medium Carbon Microalloyed Steel Wire Rod Containing Vanadium

V-microalloyed steel wire rods have being widely applied in high-rise buildings andelectric power pylon and so on. However, it is necessary to make use of V resourcereasonably and effectively, and give full paly to the influence of precipitation strength of V.In this paper, four V-microalloyed steels were taken as research objects to study the hotdeformation behaviors, phase transformation behaviors and the simulating of high lineindustrial producing. To better guide the production practice, the effect of V on the hotdeformation and phase transformation behaviors were discussed, and the influence ofcontrolled rolling and controlled cooling on microstructure and microhardness werestudied.The hot deformation and stress relaxation experiments were carried out on aGleeble-3500thermo-mechanical simulator, and the dynamic recovery(DRV), dynamicrecrystallization(DRX), static recrystallization(SRX) and strain-induced precipitation werestudied. The kinetic expressions of DRX and SRX were determined, and the Precipitationtemperature time (PTT) and Recrystallization precipitation temperature time (RPTT)curves were constructed. It was shown that V-precipitation could restrict dynamicrecrystallization, increase the peak stress and peak strain. At the same time, V-precipitationcould also restrict static recrystallization and reduce the crystallization rate. Moreover, Cand N could make the PTT curves move left, and decrease the induction period ofprecipitation.The effect of deformation condition and alloying elements on phase transformationwere studied by the kinetics of static and dynamic continuous cooling transformation, andthe CCT curves were drawed. It could be seen that the increase of V-precipitation contentmade bainite region move right, bainite transition occured at the lower cooling rate and theamount of ferrite decreased. Meanwhile, the deformation in austenite region could risephase-transition temperature and increase the amount of ferrite.The influence of four parameters, the deformation temperature, spinning temperature,cooling rate and coiling temperature, on the transformation characteristics were determined by using dilatometer test, microscopic observation and hardness mea-surement. It was shown that fine grain size was obtained at a lower deformationtemperature, as well as a lower spinning temperature and a lower coiling temperature, buta higher cooling rate. However, the grain size cannot directly determine the hardness ofthe steels, the precipitation and dislocation should be considered in the practicalproduction.